June 22, 2001
Finalizing our power plant choices raises a number of questions about gearing. Gearing is depended on tire size. Tire size effects a number of important parameters including ride height and center of gravity. It would be extremely useful to be able to model the car, and modify these interrelated parameters. In the age of computers, this is surprisingly easy and affordable to do.

For $70 ($90- a $20 rebate) we purchase a Logitech Wingman Steering Wheel. Along with the steering wheel comes a computer racing game called Sports Car GT (the game can be purchased for $19.95 alone, but what fun would it be without a steering wheel?).

This computer racing simulator features GT cars on well known tracks around the world. The program has been out a while. Skilled game hackers have dissected the software and created some very useful additions. These programs allow you to create, modify, and add cars and tracks to the program. There is also a program that allows you to tweak the settings to make the game's car behavior physics more realistic. These additions are available on the Internet for free, to anyone with the interest and patience to use them.

We set up the program following step by step instructions available at Beginner's Guide to SCGT. Next, we downloaded a couple of copies of Subaru Impreza's from Discpad's Garage. Then using a program called V-Edit (see Beginner's Guide to SCGT for location) and a program called GT Vehicle Editor or GTVE (see Beginner's Guide to SCGT for location), we modify the Subaru's parameters, such as torque curve, weight, gearing to match our plans. Finally, we adjust the game settings to make it even more realistic using a program called Advanced Options Editor from The Norway Pits.

Now, we are ready to start testing.

The first question that this simulator might help with is choosing a final drive ratio. To allow later comparisons to reality, we do our testing on a local track that our drivers are intimately familiar with, the Sebring 12 hour course. We create two versions of the ProEV Electric Imp, exactly the same except for final drive ratio. We allow them to race controlled by the computer. The winner has the better ratio. We reset their ratios based on this information and run again until we narrow it down to the best ratio (3.8).

Now, this ratio is the best for these virtual cars driven by the computer on the Sebring 12 hour course. It will be different for different drivers and different tracks, but we have a good starting point. The stock Impreza (Manual) differential is 3.9.

What testing has really helped us understand is the trade offs of the different ratios. In a single speed car (we do not use a gear box), choosing a final drive ratio is a balance of choosing a gear ratio low enough to get the acceleration out of the slow corners (~57 Mph) or a ratio long enough to continue to accelerate to a high top speed (~131Mph).

We make maximum horsepower at 5500 rpm. We need to gear the final drive to keep the car as close to this point as possible.

Testing will continue.

Click the image below to download your own copy of ProEV's virtual Electric Imp for use with the Sports Car GT racing game. Please note, the ProEV virtual Electirc Imp file in provided as a .zip file. You will need to download the Winzip utility program from here in order to unzip it.

Virtual Electric Imp

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